This invention relates to new, substantially linear polyester polyurethanes containing hydroxyl end groups, based on selected starting materials, and their use as adhesives or for the production of adhesives.
The use of substantially linear polyester polyurethanes containing hydroxyl end groups as adhesives for bonding a wide variety of materials such as PVC, natural or synthetic types of rubber containing plasticizer to materials of the same type or to other materials is known and has been described, for example, in DE-PS No. 1,256,822 and in DE-PS No. 1,930,336.
These dihydroxy polyester polyurethanes based on crystalline dihydroxy polyesters generally have a molecular weight of from 800 to 4,000, optionally low molecular weight chain lengthening agents and diisocyanates do not, however, fulfill all the requirements of modern jointing and adhesive technology in spite of their wide use in the adhesives industry.
Manufacturing methods for fashion shoes for example, require the layer of adhesive applied to the shoe soles to be rendered sufficiently thermoplastic by a brief heat shock (shock activation) to enable it to be permanently bonded to the non-activated adhesive on the uppers. For a problem-free manufacturing process, it is important that this contact adhesive time (i.e. the period of time during which the adhesive layer maintains its adhesive properties) should be sufficiently long after the shock activation. This aim has been achieved in the past by developing highly thermoplastic dihydroxy polyurethanes which although have a sufficient contact adhesive time after shock activation also have the serious disadvantage that, because of their insufficient initial strength, they require long molding times in the press, which requirement prevents efficient mass production.